I'm on reasearch using USRP and GNU radio for solar flare observation. The research is making digital radio receiver in GNU radio companion and using USRP B200. Basically the purpose of system is to receive multi-frequency which in range frequency 45-870 MHz. The problem is i can't receive signal execpt of center frequency. I want the system could be able to scan signal in those range frequency above. I want to change center frequency automatically in periodically but i don't know how the way. I'm an amateur and i haven't basic using GRC. I hope someone can help me and give me reference to solve the problem.